An electrically erasable programable read only memory (EEPROM) is a user-modifiable read-only memory that can be erased and reprogrammed repeatedly through the application of higher than normal electrical voltage. In general, EEPROM cells have proven to be a reliable and versatile form of nonvolatile reprogrammable memory.
Turning to Prior Art FIG. 1 illustrated is a conventional EEPROM device 100. The particular EEPROM device 100 shown in FIG. 1 includes a semiconductor substrate 110 having a source implant 120 and a drain implant 130 located therein. Further located within the semiconductor substrate 110, and defined by the source implant 120 and the drain implant 130, is a channel region 140. The EEPROM device 100 also includes a floating gate 150 having a dielectric layer 160 located thereon. Located on the dielectric layer 160 in FIG. 1 is a control gate 170. While the control gate 170 may comprise a multitude of different materials, metal control gates are gaining widespread use in many different technologies. Most common, however, are metal control gates comprising titanium nitride.
Despite the success of EEPROM cells as a reliable and versatile form of nonvolatile reprogrammable memory, conventional EEPROM devices, such as the one illustrated in FIG. 1, have their drawbacks. One such drawback includes the introduction of alkali ions into the dielectric layer 160 during the manufacture of the metal control gate 170. As the alkali ions are introduced into the EEPROM device 100 at an initial stage of manufacture, subsequent thermal anneal steps often drive the alkali ions into other undesirable portions of the EEPROM device 100, such as the floating gate 150. Conversely, the alkali ions tend to negatively impact the EEPROM device's data retention characteristics. It is believed that changes in the EEPROM device's threshold voltage (VT) caused by the alkali ions, possibly cause the data retention issues.
Accordingly, what is needed in the art is an EEPROM or other semiconductor device that does not suffer from the aforementioned deficiencies found in the prior art.